Dunnhumby runs Tesco's loyalty card programme, which tracks customers shopping habits to build up profiles of consumers and target them with relevant offers. The Clubcard was credited with helping Tesco overtake Sainsbury's in the 1990s to become the UK's biggest supermarket.

Given Google's interest in data and data analytics, it's easy to see the appeal of Dunnhumby for the company. It's thought the sale could pull in up to £2 billion ($3.17 billion) for Tesco. Other interested parties include Sir Martin Sorrell's giant advertising group WPP.

That said, Google acquiring Dunnhumby would be unlike any of its previous acquisitions. Dunnhumby's strength is its decades of data on more than 1 billion shoppers worldwide, and a set of advanced analytics tools that help brands set their prices, choose which products to launch next, and make decisions on setting promotions. That's a world away from the search and digital advertising business Google runs.

Integrating 26-year-old Dunnhumby and its 3,000 employees worldwide might also be a difficult cultural fit with Google.